The present invention is directed to diaphragm-type pilot-operated valves and in particular to those of the type that provide control orifices in their main diaphragms.
Pilot-operated vanes of the diaphragm type occur in widely varying configurations in which the invention to be described below can be practiced. FIG. 1 depicts one type, which is commonly used in public-facility urinals and closets. The vane 10 depicted in FIGS. 1 and 2 is shown in its closed condition, in which a diaphragm 12 is disposed on a valve seat 14 formed on the lower part 16 of a valve body that also includes an upper body part 18 comprising a dome or cap 20 that clamps the diaphragm 12 against the lower body part 16 by the action of an upper housing 22 that threadedly engages the outer surface of the lower body part 16.
In the closed position that FIG. 1 depicts, water that has entered by way of an inlet pipe 24 into an annular main chamber 26 surrounding a cylindrical inner wall 30 of the lower body part 16 is prevented by the diaphragm 12 from flowing from that main chamber 26 into an outlet conduit 32. Although the water in the main chamber 26 is under pressure, the diaphragm 12 resists the pressure because a control orifice 34 has allowed pressure equalization to occur between the main chamber 26 and a pilot chamber 36 formed by the dome 20 and the diaphragm 12; i.e., the diaphragm 12 divides into two parts a composite chamber that the valve body forms, but the control orifice tends to equalize the individual chambers' pressures.
The pressure in the pilot chamber 36 acts downward on the diaphragm 12 over an area greater than that over which the same pressure acts upward from the main chamber 26, so the force tending to keep the valve closed exceeds that tending to open it. To open this main valve, some type of pressure-relief mechanism is operated to relieve the pressure in the pilot chamber. In the illustrated example, a pilot valve described below is provided in the main diaphragm itself for this purpose, but the teachings of the invention to be described below are applicable to other types of pressure-relief mechanisms, too. In our U.S. Pat. No. 5,125,621 for a Flush System, for instance, the pressure-relief mechanism comprises a pilot valve in the cap.
The diaphragm 12 includes a disk-shaped main flexible diaphragm plate 38, to the interior of which, as is best seen in FIG. 2, is secured an elongated generally cylindrical guide member 40 by a collar 42 and a retaining ring 44. The collar 42 both stiffens the diaphragm assembly and acts as a guide by virtue of an annular guide-flange portion 46 extending upward from its upper surface. At the lower end of the lower cylindrical guide member 40 are provided spacer fins 48, which engage the lower body part's cylindrical inner wall 30 while permitting flow between the wall 30 and the cylindrical guide member 40.
To open the main valve--i.e., to permit the diaphragm assembly 12 to be lifted from the main valve seat 14 and thereby allow flow from the inlet conduit 24 to the outlet conduit 32--the pressure in the pilot chamber 36 is relieved through a relief opening 49 in the main diaphragm assembly 12 by displacing a pilot valve member 50 from a pilot seat 52 formed in the diaphragm plate 38. Specifically, operation of a lever 54 causes a plunger 56 to be driven to the left in FIG. 1 against a rod portion 58 of the valve member 50, and the resulting mechanical advantage enables the user to open the pilot valve readily against the force that the pilot-chamber pressure applies to the pilot valve member 50. Although the drawing depicts a manually operated pilot valve, those skilled in the art will recognize that pilot-valve operation is often performed automatically by a solenoid or other electromechanical operator, and it will be apparent that the invention described below is applicable to automatically operated valves, too.
When the pilot valve 50 is displaced, water flows with minimal flow resistance from the pilot chamber 36 through the relief opening 49, while the control orifice 34 in the diaphragm plate 38 imposes considerable resistance to the compensating flow from the main chamber 26 through orifice 34 to the pilot chamber 36. Consequently, the pressure in the pilot chamber decreases enough that the force exerted by it is lower than that exerted by the pressure in the main chamber 26. The portion of the diaphragm plate 38 interior to its clamped portion 59 accordingly flexes upward, rising off the main valve seat 14; i.e., the valve opens.
When the user releases the lever 54, the pilot valve 50 returns to its position on pilot valve seat 52, but the pressure in the pilot chamber 36 does not immediately return to the level in the main chamber 26, because the pressure-equalizing flow from the main chamber 26 to the pilot chamber 36 is restricted by the small size of the control orifice 34. This is desirable because it is necessary for proper urinal operation that flow continue for a predetermined length of time. Ultimately, however, the pressure difference is reduced to the point at which the downward force on the main diaphragm 12 overcomes the upward force, and the valve closes.
From the foregoing discussion, it will be appreciated that the size of the control orifice 34 has significant operational implications. Specifically, if the control orifice is too large, pressure equalization will occur too rapidly after the lever 54 is released, water hammer will result, and water will not flow for the requisite time interval. It is therefore necessary for the flow path through the orifice to be sufficiently narrow. Unfortunately, the small size of the control orifice in pilot-operated valves of this type is one of the biggest-if not the biggest-source of maintenance problems; because of its small size, the control orifice is particularly vulnerable to being clogged by water-borne particles and thus being prevented from closing the valve.